A. Smoking raises your risk of premature death, lung cancer, heart attacks, strokes, respiratory disease, and other health problems. Does your health “reset” after you quit smoking? Research has examined both the benefits of quitting smoking at various ages, and the health risks of former smokers. The main message is that quitting smoking at any time will benefit your health and extend your life, but quitting young is best.

Gregory N. Connolly, director of the Harvard School of Public Health’s Center for Global Tobacco Control, says that if you give up smoking before age 35, you have a good chance of restoring your health risks to that of a nonsmoker. A recent study on more than one million women in the United Kingdom, published in The Lancet, found that women who quit smoking before age 40 avoid more than 90 percent of the excess risk of death caused by continuing smoking, while those who stop before age 30 avoid more than 97 percent of it.

For individual diseases, the time it takes for your risk to normalize varies. Connolly says that the additional risk of heart attacks and strokes drops quickly, but lung cancer risk may take around 15 years from the time you quit to reach the levels of a lifetime nonsmoker.

Cutting back isn’t the same as quitting; based on epidemiological data, Connolly says, “it’s not how much you smoke that causes disease, it’s the number of years you smoke.”